It doesn't check if the GMEXP_CFG exists so on a new install where the game has created the placeholder (GMEXP_CFG = nil) but you haven't assigned a table to it, this will fail.
Lua Code:
if event == "PLAYER_LOGIN" then
if not GMEXP_CFG then
GMEXP_CFG = {}
end
-- etc.
end
With your code, if a user sets a setting to nil it will be reset on next login which is probably not desired and depends on your configuration setup.